How to use the sewing pattern scaling calculator
- Choose Resize to a target to find the percentage, or Apply a percentage if you already know it.
- For a target, enter a current measurement on the pattern and the wanted measurement in the same unit.
- Optionally enter a piece measurement to see how long it becomes after scaling.
- Read the headline for the copy percentage. The table shows what a second copy at another percentage does to the total.
Formula
scale % = wanted measurement / current measurement x 100
new length = length x scale % / 100
area scale = (scale % / 100) squared
Every length changes by the same factor, so the area changes by the square of it. A percentage above 100 enlarges the pattern, and one below 100 reduces it.
Enlarging a pattern from 8 to 10 inches
10 / 8 x 100 = 125%. Every length is multiplied by 1.25, so a 6 inch piece becomes 7.5 inches. The area is multiplied by 1.25 x 1.25 = 1.5625, so the pattern covers 156.25% of the original area.
Reducing from 8 to 6 inches gives 6 / 8 x 100 = 75%, which reduces the pattern by 25% and turns the 6 inch piece into 4.5 inches. Copying a 125% enlargement again at 150% gives a total scale of 187.5%.
Checking a scaled pattern
Printers and copiers do not always reproduce a percentage exactly, and paper can stretch or shrink slightly. Many patterns include a scale bar or a test square. After copying, measure it with a ruler and compare it with the size it should be. If it is off, adjust the percentage and copy again before you cut any fabric.
Scaling changes every dimension equally, so it does not fix a pattern that does not fit a body or a project. It is for making the same design larger or smaller, such as fitting a design to a different size of item.
Big prints and related tools
A large enlargement may not fit on one sheet. The Poster Printer and Tiler splits a big image into sheets you can tape together. For proportions, see the Aspect Ratio Calculator and the Scale Model Converter.
Assumptions and limits
- The measurement used for the percentage is accurate, and the pattern should be scaled equally in both directions.
- Both measurements must be above zero and in the same unit.
- Total scale for a second copy multiplies the two percentages.
- Results are shown to two decimals.
Frequently asked questions
How do I find the percentage to enlarge a pattern?
Divide the size you want by the size it is now and multiply by 100. To take a pattern from 8 inches to 10 inches, 10 / 8 x 100 = 125%. Copy it at 125% and then measure the result.
Why does the area change more than the percentage?
Because the area depends on length times width, and both change. A 125% copy makes each side 1.25 times longer, so the area is 1.25 x 1.25 = 1.5625 times larger, which is 156.25%.
How do I scale a pattern down?
Use a wanted size that is smaller than the current one. Going from 8 inches to 6 inches is 75%. The page then says the pattern is reduced by 25%.
What if I copy the pattern twice?
The percentages multiply. A 125% copy followed by a 150% copy gives 1.25 x 1.5 = 1.875, or 187.5%. The table on the page shows the total for several second-copy percentages.